Many olefin polymerization catalysts are known, including conventional Ziegler-Natta catalysts. While these catalysts are inexpensive, they exhibit low activity and are generally poor at incorporating α-olefin comonomers. To improve polymer properties, single-site catalysts, in particular metallocenes are beginning to replace Ziegler-Natta catalysts.
Catalyst precursors that incorporate a transition metal and an indenoindolyl ligand are known. U.S. Pat. Nos. 6,232,260 and 6,451,724 disclose the use of transition metal catalysts based upon indenoindolyl ligands, but have no examples using supported catalysts. While they mention that supported catalysts may be used, little information is given about the preparation of the supported catalysts.
WO 01/53360 discloses open architecture indenoindolyl catalysts that may be supported. In the single example (Example 8) preparing a supported catalyst, a solution of the catalyst is added to a polyethylene support.
U.S. Pat. No. 6,559,251 discloses a process for polymerizing olefins with a silica-supported, indenoindolyl Group 4-6 transition metal complex having open architecture.
U.S. Pat. No. 6,541,583 discloses a process for polymerizing propylene in the presence of a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands. None of the examples uses a supported catalyst. They state that the catalyst can be immobilized on a support but give no process details.
U.S. Pat. No. 6,211,311 prepares supported catalysts containing heteroatomic ligands. The support is chemically modified with an organoaluminum, organosilicon, organomagnesium or organoboron compound for improved catalyst stability and activity. There is no indication that zinc compounds may be used, and there is no indication that increased polymer molecular weight may be obtained.
Pending application Ser. No. 10/123,774, filed Apr. 16, 2002, discloses a process for polymerizing ethylene in the presence of a silica-supported Group 3-10 transition metal catalyst that has two bridged indenoindolyl ligands. This application teaches that the silica can be chemically treated and points to the above-mentioned U.S. Pat. No. 6,211,311.
Organozinc compounds such as diethylzinc have been used in olefin polymerizations as chain transfer agents to lower molecular weight. For example, U.S. Pat. Nos. 6,524,986; 6,489,408; 6,476,173 and 6,221,802 mention the use of diethylzinc to control molecular weight by acting as a chain transfer agent similarly to how hydrogen is often used to lower molecular weight. None teaches treatment of a support with an organozinc compound prior to combining it with an organometallic complex.
Macromolecules 27 7938-7940 (1994) teaches polymerization of methyl methacrylate by dicyclopentadienyldimethyl zirconium by reacting the methyl methacrylate with diethylzinc prior to unsupported catalyst addition and polymerization.
U.S. Pat. No. 6,177,527 teaches an olefin polymerization process using racemic and meso stereoisomers of a metallocene catalyst containing two cycloalkadienyl ligands. They state that it is preferred not to use a support, but give a long list of possible supports including silica with diethylzinc. No further teachings are found nor are the catalysts used based upon indenoindolyl systems.
Despite the considerable work that has been done with catalysts based upon indenoindolyl ligands there is a need for improvement, especially with regard, to increasing activity and molecular weight. Organozinc compounds have apparently not been used in conjunction with organometallic complexes that incorporate indenoindolyl ligands. When organozinc compounds are mentioned for use in olefin polymerizations with metallocene catalysts they act as chain transfer agents and reduce polyolefin molecular weight, the opposite of the effect I have found with complexes containing indenoindolyl ligands.